1. Field of the Invention
The present invention relates to a USB controller used for connecting a peripheral device according to the USB standard to a computer. More particularly, the invention relates to a USB controller which eliminates time and effort to make a peripheral device usable.
2. Description of the Related Art
Recently, a novel standard called a USB (Universal Serial Bus) adapted to a personal computer has made its appearance. In compliance with the novel standard, connectors of the same shape of various peripheral devices such as a keyboard, a mouse, and a game pad are formed. The peripheral devices are used by connecting the connectors to USB ports of a personal computer. Peripheral devices adapted to the USB standard have also come to be distributed in the market.
The USB port has therein four pins of a pin for a D+ data line, a pin for a D- dataline, a pin for power supply, and a pin for the ground. Either the D+ or D- pin is used and is pulled up (switched on), thereby recognizing connection of a device (peripheral device). By making either the D+ or D- pin pulled down (switched off), it is recognized that the device is not connected.
Although usually about two of the same USB ports are provided for a single personal computer, when three or more peripheral devices adapted to the USB are connected, the number of ports are short for the connectors.
In order to cope with the case, a device called a USB hub (not shown) in which a plurality of USB ports having the same shape as that of the USB port formed on the personal computer side are formed has developed. By inserting the device into the USB port on the personal computer side, a plurality of peripheral devices can be connected to the single USB port on the personal computer side.
In case of connecting peripheral devices to the USB ports formed in the main unit of a personal computer, however, whenever a peripheral device is added or eliminated, the peripheral device cannot be used unless the user performs an operation for pulling out the USB connector of the peripheral device connected to the USB port of the personal computer and then re-inserting the USB connector, thereby allowing the newly connected peripheral device to be re-recognized.
When the USB port is formed on the rear side of the personal computer, the user has to go to the rear side of the personal computer and pull out and insert the USB connector, so it is very troublesome.
That is, when the peripheral device is added or disconnected, by pulling down the D+ pin (or D- pin) in the USB port which has been pulled up and again pulling it up, information of each peripheral device connected at the time point when the D+ pin is pulled up again is transmitted to the personal computer side through a data line, so that the connecting state of the peripheral devices can be re-recognized.
On the other hand, in case of not performing the pull-out and insertion of the USB connector, a method of re-recognizing devices by resetting the system on the personal computer side can be employed. In this case, however, there is a problem that it takes time to make the personal computer operable again and the operation is troublesome. When the system is reset, inconveniences such that presently used application software has to be finished are caused.
The USB hub simply increases the number of devices which can be connected. Even if the USB hub is used, in a manner similar to the case where the USB hub is not used, there is a drawback that the USB connector has to be pulled out and inserted or the system has to be reset when the peripheral device is added or eliminated.
Especially, when the peripheral device is wireless, since there is no cable, it has an advantage of easy handling. In this case as well, however, the connector has to be pulled out and inserted for re-recognition of the peripheral devices, so that further improvement in the operability utilizing the advantage of being wireless of the device cannot be expected.